As one of a method of treating radioactive liquid waste containing radioactive nuclides which are generated in nuclear facilities, for example, nuclear power plants, an adsorption treatment method in which radioactive nuclides are removed from radioactive liquid waste using an ion exchange resin or the like is exemplified. This adsorption treatment method is a treatment method of removing ionic radioactive nuclides through adsorption using an inorganic or organic adsorbent or an ion exchange resin.
It is assumed that radioactive liquid waste generated in nuclear facilities have various properties (containing components, the pH value, and the like). For example, acidic radioactive liquid waste and alkaline radioactive liquid waste can be considered. Further, depending on an adsorbent, it is necessary for the adsorbent to have an appropriate pH region in order to exhibit adsorption performance. In a case where such an adsorbent is selected, a treatment in which the pH of radioactive liquid waste is adjusted to acidic or alkaline according to the adsorbent, and then radioactive nuclides contained in the radioactive liquid waste are adsorbed by the adsorbent, is performed in some cases. In both acidic and alkaline radioactive liquid waste, it is considered that the pH of the radioactive liquid waste after the adsorption treatment is performed may vary according to the properties at the time when the radioactive liquid waste was generated, radioactive nuclides to be contained therein, or the selected adsorbent.
For a treatment of the radioactive liquid waste after the radioactive nuclides are removed, various options such as concentration volume reduction, storage, solidification, or release out of the system (for example, to the environment) may be considered. In all cases, the treatments are performed after the pH of the radioactive liquid waste is adjusted close to neutral. Accordingly, in a case where the pH of the radioactive liquid waste after the adsorption treatment is performed on the radioactive nuclides is out of the neutral region (for example, pH 4 to pH 9), a process of adjusting the pH of the radioactive liquid waste needs to be carried out. When the radioactive liquid waste becomes acidic, a treatment of adding an alkali or a deacidification treatment is performed. When the radioactive liquid waste is alkaline, the radioactive liquid waste is required to be neutralized by adding an acid.
An example of the treatment method of adsorbing and removing radioactive nuclides from radioactive liquid waste is described in Ikeda et al., Proceedings of GLOBAL 2011, Dec. 11 to 16, 2011, Makuhari, Japan, USA, Paper No. 524705 (2011). In the treatment method of adsorbing and removing the radioactive nuclides, ionic radioactive nuclides contained in radioactive liquid waste are adsorbed by an adsorbent and then removed by allowing the radioactive liquid waste to pass through a container filled with the adsorbent. Further, before the radioactive liquid waste is supplied to the container filled with the adsorbent, a particulate substance contained in the radioactive liquid waste is removed using a filtration device.
Moreover, for example, JP-A-2013-57599 describes a method of treating radioactive liquid waste. Radioactive cesium contained in radioactive liquid waste is adsorbed by iron ferrocyanide by adding the iron ferrocyanide to a container in which radioactive liquid waste flows and then radioactive strontium contained in the radioactive liquid waste is adsorbed by a zeolite-based adsorbent by adding the zeolite-based adsorbent to the radioactive liquid waste in the container. In addition, an inorganic coagulant is added to the radioactive liquid waste. Due to the action of the inorganic coagulant, aggregates of solid particles, containing particles of the iron ferrocyanide to which radioactive cesium is adsorbed and particles of the zeolite-based adsorbent to which radioactive strontium is adsorbed, are formed and the aggregates are precipitated and separated.
Further, in a method of treating radioactive liquid waste described in JP-A-2002-31697, a filtration device and an ion exchange device are used. An ultrafiltration membrane is used as the filtration device. Colloid components contained in radioactive liquid waste are removed by the ultrafiltration membrane and then ionic radioactive nuclides contained in the radioactive liquid waste are removed by the ion exchange device. In a method of treating radioactive liquid waste described in JP-A-2013-108808, colloid components contained in radioactive liquid waste are removed by a filtration device (for example, an ultrafiltration membrane). The radioactive liquid waste is supplied to the filtration device after sodium hydroxide is added to the radioactive liquid waste and the pH of the radioactive liquid waste is adjusted to a predetermined value. The radioactive liquid waste from which colloids are removed by the filtration device is supplied to an adsorption tower filled with a titanate-based adsorbent. Since the titanate-based adsorbent can easily adsorb strontium, the strontium contained in the radioactive liquid waste is removed in the adsorption tower.
Moreover, in a case where radioactive liquid waste contains salts at a high concentration, the adsorption of radioactive nuclides may be disturbed by the salts.
Meanwhile, in a method of treating radioactive liquid waste described in JP-A-61-40593, a powdery (or particulate) substance that adsorbs radioactive nuclides is added to radioactive liquid waste by performing a reaction of forming radioactive nuclides and chelate and then the substance to which the radioactive nuclides are adsorbed is separated out through filtration.
Further, JP-A-2013-170959 describes a method of treating radioactive liquid waste in which an oxidizing agent or a reducing agent is added to radioactive liquid waste containing radioactive nuclides and the radioactive nuclides are adsorbed and removed by an adsorbent. Moreover, JP-A-2013-170959 describes a method of treating radioactive liquid waste in which an oxidizing agent or a reducing agent is added to radioactive liquid waste containing radioactive nuclides, a pH adjusting agent is added thereto, and then the radioactive nuclides are adsorbed and removed by an adsorbent and a method of treating radioactive liquid waste in which a pH adjusting agent is added to radioactive liquid waste containing radioactive nuclides and then the radioactive nuclides are adsorbed and removed by an adsorbent.